Intra-body device communication with redundant message transmission

ABSTRACT

Implantable medical devices (IMD), such as but not limited to leadless cardiac pacemakers (LCP), subcutaneous implantable cardioverter defibrillators (SICD), transvenous implantable cardioverter defibrillators, neuro-stimulators (NS), implantable monitors (IM), may be configured to communicate with each other. In some cases, a first IMD may transmit instructions to a second IMD. In order to improve the chances of a successfully received transmission, the first IMD may transmit the instructions several times during a particular time frame, such as during a single heartbeat. If the second IMD receives the message more than once, the second IMD recognizes that the messages were redundant and acts accordingly.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of co-pending U.S. patent applicationSer. No. 15/880,136, filed Jan. 25, 2018, which claims the benefit ofU.S. Provisional Patent Application Ser. No. 62/450,833, filed on Jan.26, 2017, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains to medical devices, and moreparticularly to wireless intra-body communication between medicaldevices.

BACKGROUND

Implantable medical devices are commonly used today to monitorphysiological or other parameters of a patient and/or deliver therapy toa patient. For example, to help patients with heart related conditions,various medical devices (e.g., pacemakers, defibrillators, etc.) can beimplanted in a patient's body. Such devices may monitor and in somecases provide electrical stimulation (e.g. pacing, defibrillation, etc.)to the heart to help the heart operate in a more normal, efficientand/or safe manner. In another example, neuro stimulators can be used tostimulate tissue of a patient to help alleviate pain and/or othercondition. In yet another example, an implantable medical device maysimply be an implantable monitor that monitors one or more physiologicalor other parameters of the patient, and communicates the sensedparameters to another device such as another implanted medical device oran external device. In some cases, two or more devices cooperate tomonitor and/or to provide therapy. In many of these examples, there is adesire to have such devices communicate with other devices when needed.

SUMMARY

The present disclosure pertains to medical devices, and moreparticularly to wireless intra-body communication between medicaldevices. The medical devices may include implantable medical devices(IMD), such as but not limited to leadless cardiac pacemakers (LCP),implantable cardioverter defibrillators (ICD), subcutaneous implantablecardioverter defibrillators (SICD), extracardiac implantablecardioverter defibrillators, transvenous implantable cardioverterdefibrillators, neuro-stimulators (NS), implantable monitors (IM),and/or the like. In some cases, the medical devices may include one ormore external medical devices such as device programmers, wearabledefibrillators and/or other external medical devices.

In one example, an implantable medical device (IMD) may be configured topace a patient's heart and to be disposable within a chamber of thepatient's heart. The IMD may include a housing and a plurality ofelectrodes. A controller may be housed by the housing and may beoperably coupled to the plurality of electrodes. In some cases, thecontroller may be configured to generate and deliver pacing pulses via apair of the plurality of electrodes, to receive messages transmitted byconducted communication from a remote implantable medical device (IMD)via a pair of the plurality of electrodes, and to receive cardiacsignals via a pair of the plurality of electrodes. The controller mayalso be configured to receive at least one of a plurality oftransmissions of the same message transmitted by conducted communicationby the remote IMD during a cardiac cycle, and when more than one of theplurality of transmissions of the same message are received by thecontroller during the cardiac cycle, the controller may be configured totreat the more than one transmissions of the same messages ascommunication of one message.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to institute a blanking period during thecardiac cycle during which received cardiac signals are ignored by thecontroller.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to receive at least one of a plurality oftransmissions of the same message during the blanking period.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to institute the blanking period at apredetermined time following a detected R-wave in the received cardiacsignal.

Alternatively or additionally to any of the embodiments above, theblanking period may be configured to extend over at least 10 percent ofa cardiac cycle, but less than an entire cardiac cycle.

Alternatively or additionally to any of the embodiments above, theblanking period may be configured to extend over at least 20 percent ofa cardiac cycle, but less than an entire cardiac cycle.

Alternatively or additionally to any of the embodiments above, theplurality of transmissions of the same message are received over a timeduration that allows for physiological changes in the patient thatresult in differing communication vectors.

Alternatively or additionally to any of the embodiments above, the timeduration may be selected to accommodate physiological changes in thepatient resulting from the patient's heart beating.

Alternatively or additionally to any of the embodiments above, the timeduration may be selected to accommodate physiological changes in thepatient resulting from the patient breathing.

Alternatively or additionally to any of the embodiments above, the timeduration may be shorter than a cardiac cycle.

Alternatively or additionally to any of the embodiments above, the timeduration may span more than one cardiac cycle.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to institute a blanking period in responseto receiving a message.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to generate and deliver pacing pulses via afirst pair of the plurality of electrodes, to receive messagestransmitted from the remote IMD via a second pair of the plurality ofelectrodes and to receive cardiac signals via a third pair of theplurality of electrodes, where the first pair of electrodes, the secondpair of electrodes and the third pair of electrodes correspond to thesame pair of electrodes.

Alternatively or additionally to any of the embodiments above, themessage may be a command.

Alternatively or additionally to any of the embodiments above, thecommand may be an ATP command that instructs the controller to deliverAnti-Tachycardia Pacing (ATP) therapy to the patient's heart via a pairof the plurality of electrodes.

In another example, an implantable medical device (IMD) may beconfigured to sense electrical cardiac activity of a patient's heart andto deliver therapy to the patient's heart. The IMD may include ahousing, a plurality of electrodes, and a controller that is housed bythe housing and operably coupled to the plurality of electrodes. Thecontroller may be configured to sense cardiac electrical activity viatwo or more of the plurality of electrodes and to deliver therapy viatwo or more of the plurality of electrodes. In some cases, thecontroller may be configured to analyze the sensed cardiac electricalactivity and to make a determination as to whether to provide a messageto a remote implantable medical device (IMD) secured to the patient'sheart. When the controller makes a determination to provide a message tothe remote IMD, the controller may be configured to transmit a pluralityof transmissions of the message by conducted communication during acardiac cycle of the patient's heart.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to add a tracking number to each of theplurality of transmissions of the message.

Alternatively or additionally to any of the embodiments above, the IMDmay be incapable of receiving a conducted communication messages fromthe remote IMD.

Alternatively or additionally to any of the embodiments above, each ofthe plurality of redundant transmissions of the message may include acommand to the remote IMD to deliver one or more pacing pulses, and thecontroller of the IMD may be configured to monitor cardiac electricalactivity for an indication that the remote IMD delivered the one or morepacing pulses.

Alternatively or additionally to any of the embodiments above, after thecontroller makes a determination to provide a message to the remote IMD,the controller may be configured to transmit the plurality of redundanttransmissions of the message within a communication time period, whereinthe communication time period has a time duration is sufficiently longto allows the remote IMD to change orientations relative to the IMD as aresult of physiological changes in the patient to result in asubstantially different signal strength at the remote IMD.

In another example, a medical system for sensing and regulating cardiacactivity of a patient may include an implantable cardioverterdefibrillator (ICD) that is configured to sense electrical cardiacactivity of a patient's heart and to deliver therapy to the patient'sheart, and a leadless cardiac pacemaker (LCP) that is configured to pacea patient's heart. The ICD may include a housing, a plurality ofelectrodes and an ICD controller that is housed by the housing of theICD and operably coupled to the plurality of electrodes of the ICD. TheICD controller may be configured to sense cardiac electrical activityvia two or more of the plurality of electrodes of the ICD and to delivertherapy via two or more of the plurality of electrodes of the ICD. Insome cases, the ICD controller may be further configured to analyze thesensed cardiac electrical activity and to make a determination as towhether to instruct a leadless cardiac pacemaker (LCP) to providetherapy to the patient's heart. When the ICD controller makes adetermination to instruct the LCP to provide therapy to the patient'sheart, the ICD controller may be configured to transmit a plurality oftransmissions of an instruction during a single cardiac cycle of thepatient's heart.

The LCP may include a housing, a plurality of electrodes that areexposed external to the housing of the LCP, and an LCP controller thatis housed by the housing of the LCP and is operably coupled to theplurality of electrodes of the LCP. In some cases, the LCP controllermay be configured to generate and deliver pacing pulses via two or moreof the plurality of electrodes of the LCP, receive messages transmittedvia two or more of the plurality of electrodes of the LCP, and receivecardiac signals via two or more of the plurality of electrodes of theLCP. The LCP controller may be further configured to receive at leastone of the plurality of redundant transmissions of the instructiontransmitted by the SICD during the single cardiac cycle, and when morethan one of the plurality of redundant transmissions of the instructionare received by the LCP controller during the single cardiac cycle, theLCP controller may be configured to treat the more than one redundanttransmissions of the instruction as one instruction, and only executesthe one instruction and not each of the plurality of redundanttransmissions of the instruction.

The above summary of some illustrative embodiments is not intended todescribe each disclosed embodiment or every implementation of thepresent disclosure. The Figures, and Detailed Description, which follow,more particularly exemplify some of these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description in connection with the accompanyingdrawings, in which:

FIG. 1 is a highly schematic diagram of an illustrative system inaccordance with an example of the disclosure;

FIG. 2 is a high schematic diagram of an illustrative system inaccordance with an example of the disclosure;

FIG. 3 is a schematic block diagram of an illustrative leadless cardiacpacemaker (LCP) useable in the systems of FIGS. 1 and 2;

FIG. 4 is a schematic block diagram of an illustrative implantablecardioverter defibrillator (ICD) useable in the systems of FIGS. 1 and2;

FIGS. 5A and 5B are schematic illustrations of illustrative blankingperiods relative to an electrocardiogram (ECG);

FIG. 6 is a schematic illustration of a communication of redundantmessages within a blanking period;

FIG. 7 is a more detailed schematic block diagram of an illustrative LCPin accordance with an example of the disclosure;

FIG. 8 is a schematic block diagram of another illustrative medicaldevice that may be used in conjunction with the LCP of FIG. 7;

FIG. 9 is a schematic diagram of an exemplary medical system thatincludes multiple LCPs and/or other devices in communication with oneanother; and

FIG. 10 is a schematic diagram of a system including an LCP and anothermedical device, in accordance with an example of the disclosure.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the disclosureto the particular embodiments described. On the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the spirit and scope of the disclosure.

DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about,” whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”,“some embodiments”, “other embodiments”, etc., indicate that theembodiment described may include one or more particular features,structures, and/or characteristics. However, such recitations do notnecessarily mean that all embodiments include the particular features,structures, and/or characteristics. Additionally, when particularfeatures, structures, and/or characteristics are described in connectionwith one embodiment, it should be understood that such features,structures, and/or characteristics may also be used connection withother embodiments whether or not explicitly described unless clearlystated to the contrary.

The following detailed description should be read with reference to thedrawings in which similar structures in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of thedisclosure. While the present disclosure is applicable to any suitableimplantable medical device (IMD), the description below often usespacemakers and more particularly leadless cardiac pacemakers (LCP) asparticular examples.

FIG. 1 is a schematic diagram showing an illustrative system 10 that maybe used to sense and/or pace a heart H. In some cases, the system 10 mayalso be configured to shock the heart H. The heart H includes a rightatrium RA and a right ventricle RV. The heart H also includes a leftatrium LA and a left ventricle LV. In some cases, the system 10 mayinclude a medical device that provides anti-arrhythmic therapy to theheart H. In some cases, the system 10 may include a first medical device12 and a second medical device 14. In some instances, the first medicaldevice 12 may be implantable within the patient at a position near oreven within the heart H. In some cases, the second medical device 14 maybe implanted within the patient but at a location that is exterior tothe heart H. For example, in some cases, the second medical device 14may be implanted at a subcutaneous position within the patient's chest.In some cases, the second medical device 14 may be exterior to thepatient.

In some cases, the second medical device 14 may be configured tomaintain and/or trend pace settings and capture data for the firstmedical device 12 for the purposes of long-term optimization of pacesettings. In some cases, the second medical device 14 may utilizeadditional inputs, such as posture, time of day, intrinsic heart rate,and the like, as inputs to a capture algorithm. The second medicaldevice 14 may, for example, be configured to correlate changes in a pacethreshold resulting from the other inputs, and proactively adjust pacesettings. In some cases, the second medical device 14 may be utilized tooptimize the AV delay utilized by the first medical device 12. Forexample, the second medical device 14 may be able to monitor ECGmorphology and/or acceleration data, such as RV or LV pace timing.

If the second medical device 14 is implanted prior to implanting thefirst medical device 12, the second medical device 14 may be used toguide optimal placement of the first medical device 12 by, for example,monitoring the QRS width, morphology, Heart Rate Variability (HRV),accelerometer signals, etc. In some cases, the second medical device 14could provide feedback of the attempted first medical device 12'slocation prior to fixation or untethering of the first medical device12. Minimizing QRS width, HRV and/or certain morphological parameterswould be a possible goal of the clinician to obtain such an optimalimplantation site, for example. In some cases, the second medical device14 may be able to monitor the impedance and or heart sounds to possiblydetect myocardial functional improvements as indicated by hypertrophy,or dilated cardiomyopathy. For example, these diseases generally haveincreased left ventricles, thus possibly lower impedance and/orcontraction changes. These are just examples.

FIG. 2 is a schematic diagram showing an illustrative system 16 that maybe used to sense and/or pace a heart H. In some cases, the system 16 maybe considered as being an example of the system 10 shown in FIG. 1. Insome cases, the system 16 may include a leadless cardiac pacemaker (LCP)18 and an implantable cardioverter defibrillator (ICD) 20. In somecases, the ICD 20 may be a subcutaneous implantable cardioverterdefibrillator (SICD), an extracardiac implantable cardioverterdefibrillator and/or a transvenous implantable cardioverterdefibrillator. In some cases, as illustrated, the ICD 20 may be an SICD.The LCP 18 may be considered as being an illustrative but non-limitingexample of the first medical device 12 and the ICD 20 may be consideredas being an illustrative but non-limiting example of the second medicaldevice 14 described with respect to FIG. 1.

In some cases, the LCP 18 may be intracardially implanted. While asingle LCP 18 is shown in FIG. 2, it will be appreciated that two ormore LCPs 18 may be implanted in or on the heart H. The LCP 18 may beimplanted into any chamber of the heart, such as the right atrium RA,the left atrium LA, the right ventricle RV and the left ventricle LV.When more than one LCP is provided, each LCP may be implanted in adifferent chamber. In some cases, multiple LCP's may be implanted withina single chamber of the heart H.

In some cases, the ICD 20 may be extracardially implanted. While notshown in FIG. 2, in some cases the ICD 20 may include a lead/electrodethat may be configured to be placed subcutaneously and outside of apatient's sternum. In other cases, the lead/electrode may extend aroundor through the sternum and may be fixed adjacent an inner surface of thesternum. In both cases, the lead/electrode is positioned extracardially(outside of the patient's heart). The ICD 20 may be configured to senseelectrical activity generated by the heart H as well as provideelectrical energy to the heart H in order to shock the heart H from anundesired heart rhythm to a desired heart rhythm.

In some cases, the LCP 18 and the ICD 20 may be implanted at the sametime. In some instances, depending on the cardiac deficiencies of aparticular patient, the ICD 20 may be implanted first, and one or moreLCPs 18 may be implanted at a later date if/when the patient developsindications for receiving cardiac resynchronization therapy and/or itbecomes necessary to pace the heart H. In some cases, it is contemplatedthat one or more LCPs 18 may be implanted first, in order to sense andpace the heart H. When a need for possible defibrillation becomesevident, the ICD 20 may subsequently be implanted. Regardless ofimplantation order or sequence, it will be appreciated that the LCP 18and the ICD 20 may communicate with each other using any desiredcommunications modality, such as conducted communication, inductivecommunication, acoustic communication, RF communication, opticalcommunication and/or using any other suitable communication modality.

In some cases, the LCP 18 and the ICD 20 may work together in deliveringtherapy to the heart H. For example, in some cases, the ICD 20 may sensecardiac electrical activity of the heart H and may analyze the sensedcardiac electrical activity in order to determine whether the ICD 20itself should deliver therapy such as shocking therapy to the heart H orif it would be appropriate for the ICD 20 to instruct the LCP 18 todeliver pacing therapy to the heart H. In some cases, the pacing therapymay be anti-tachycardia pacing (ATP) therapy, but this is just anexample. When the ICD 20 determines that it would be appropriate to havethe LCP 18 deliver pacing therapy, the ICD 20 may transmit a message tothe LCP 18 instructing the LCP 18 to delivery pacing therapy.

In some cases, it will be appreciated that communication vectors betweenthe ICD 20 and the LCP 18 may be at least somewhat time-dependent,particularly as the LCP 18 may be moving as a result of physiologicalchanges in the patient, such as but not limited to the heart H beatingand/or the patient breathing. For example, as the heart H beats, it willbe appreciated that an LCP 18, if anchored at its distal end to a heartwall of the heart H, can change orientation in response to the heartwall moving, blood flowing through the heart, and the like. In somecases, communication from the ICD 20 to the LCP 18 may be one-waycommunication, wherein the ICD 20 is not able to receive confirmationmessages from the LCP 18, and/or the LCP 18 is not able to transmitconfirmation messages back to the ICD 20, either as a result of hardwarelimitations or poor communication vectors, for example.

In some instances, and to help improve the robustness and/or reliabilityof the one-way communication channel, the ICD 20 may transmit aplurality of redundant transmissions of an instruction or other messageto the LCP 18. As a non-limiting example, the ICD 20 may be configuredto transmit the same instruction three times. As long as at least one ofthe three redundant messages is successfully received by the LCP 18, theLCP 18 is able to carry out the instruction received from the ICD 20. Insome cases, the plurality of redundant transmissions from the ICD 20 maybe transmitted within a single cardiac cycle. Since the orientation ofthe LCP 18 relative to the ICD 20 may change over the course of aheartbeat, the communication vector between the LCP 18 and the ICD 20may change over the course of a heartbeat. By transmitting redundantmessages, the chance that the LCP 18 is not located along a null of thetransmission field generated by the ICD 20 is increased for at least oneof the messages, thereby potentially increasing the robustness and/orreliability of the communication channel. In some cases, the pluralityof redundant transmissions from the ICD 20 are transmitted within aportion of a single cardiac cycle, such as in 10 percent, 20 percent, 30percent, 40 percent, 60 percent, or more or less.

Similarly, the LCP 18 may be configured to receive one or more of theredundant messages transmitted by the ICD 20 and to recognize that anyof the received messages are in fact redundant and represent repetitionof a single instruction and/or message, rather than multipleinstructions and/or messages. Accordingly, the LCP 18 may be configuredto treat the more than one redundant instruction, if the LCP 18successfully receives more than one redundant instruction, as a singleinstruction. As a result, the LCP 18 may only execute one instruction,and not each of the received redundant instructions. In some cases,particularly if the LCP 18 is not able to confirm receipt ofinstructions, or the ICD 20 is not able to receive such confirmatory oracknowledgement messages, the ICD 20 may monitor cardiac electricalactivity for indications that the LCP 18 carried out the desiredinstruction(s). For example, the ICD 20 may monitor cardiac electricalactivity for indications of an Anti-Tachycardia Pacing (ATP) therapy ifthe ICD 20 instructed the LCP 18 to carry out an ATP therapy.

FIG. 3 is a schematic diagram of an illustrative leadless cardiacpacemaker (LCP) 30 that may be considered as being an example of the LCP18 (FIG. 2). In some cases, the LCP 30 may include a housing 32 and aplurality of electrodes that are exposed external to the housing 32. Asillustrated, the LCP 30 includes a pair of electrodes 34, 36 that aresecured relative to the housing 32. While two electrodes 34, 36 areillustrated, it will be appreciated that in some cases the LCP 30 mayinclude three or more electrodes. A controller 38 is disposed within thehousing 32 and may be operably coupled to the pair of electrodes 34, 36via electrical connectors 35 and 37, respectively. A power supply 40 isoperably coupled to the controller 38 and provides power for operationof the controller 38 as well as providing power for generating pacingpulses that can be delivered via the pair of electrodes 34, 36 via thecontroller 38. In some cases, the controller 38 may be considered asbeing configured to generate and deliver a plurality of pacing pulsesvia the pair of electrodes 34, 36. In some cases, the LCP 30 may includeone or more other sensors such as an accelerometer or a gyro, forexample.

In some cases, the LCP 30 may include a communications module 42 that isoperably coupled to the controller 38 and may be configured to receivemessages from other devices, and in some cases send messages to otherdevices. In some cases, the communications module 42 may enable the LCP30 to receive messages from another implanted device, such as but notlimited to an SICD such as the ICD 20 (FIG. 2). In some cases, thecontroller 38 may be configured to receive, via the communicationsmodule 42, messages communicated via conducted communication that may bepicked up by the electrodes 34, 36. In some cases, the messages receivedby the LCP 18 may represent a command from a remote device such as theICD 20. In some instances, the command may be an ATP command thatinstructs the controller 38 to deliver Anti-Tachycardia Pacing (ATP)therapy to the patient's heart H via a pair of the plurality ofelectrodes.

In some cases, the controller 38 may be configured to receive at leastone of a plurality of redundant transmissions of the same messagetransmitted by conducted communication by a remote device such as theICD 20 during a cardiac cycle. When more than one of the plurality ofredundant transmissions of the same message are received by thecontroller 38 during the cardiac cycle, the controller 38 may beconfigured to treat the more than one redundant transmissions of thesame messages as one message. In some cases, the controller 38 may beconfigured to institute a blanking period within a cardiac sense channelduring the cardiac cycle during which cardiac signals sensed by theelectrodes 34 and 36 are ignored by the controller 38, meaning that thecontroller 38 is only listening for transmitted messages, and isignoring cardiac electrical activity during the blanking period. In someinstances, the controller 38 may be configured to institute a blankingperiod within the cardiac sense channel at a predetermined timefollowing a detected R-wave in the received cardiac signal. In somecases, the controller 38 may be configured to institute a blankingperiod within the cardiac sense channel in response to receiving amessage, possibly to see if additional messages are to be transmitted,for example. In some cases, the controller 38 may be configured toreceive at least one of a plurality of redundant transmissions of thesame message during the blanking period, and in some cases, may receivetwo or more of the plurality of redundant transmissions. In some cases,the controller 38 may be configured to institute a blanking periodwithin a telemetry sense channel after recognizing receipt of atransmitted message.

By instituting a blanking period within the telemetry sense channel, thecontroller 38 may be prevented from seeing or acting upon redundanttransmissions of the same message that was already received. In somecases, whether referring to the cardiac sense channel and/or thetelemetry sense channel, a blanking period may refer to a period of timeduring which corresponding sense signals/transmissions are either notsensed (e.g. sense amplifiers are turned off, signals are filtered out,etc.) or are sensed but not acted upon (e.g. signals are sensed butignored by the controller 38).

In some cases, the plurality of redundant transmissions of the samemessage may be received over a time duration that allows forphysiological changes in the patient that result in differingcommunication vectors for each of the redundant messages. When ablanking period is provided, this time duration may correspond to theblanking period, or may lie at least partially outside the blankingperiod. In some cases, the time duration may be selected to accommodatephysiological changes in the patient resulting from the patient's heartbeating. In some cases, the time duration may be selected to accommodatephysiological changes in the patient resulting from the patientbreathing. In some instances, the time duration may be shorter than acardiac cycle. In some cases, the time duration may span more than onecardiac cycle.

In some cases, the controller 38 of the LCP 30 may be configured togenerate and deliver pacing pulses via a first pair of the plurality ofelectrodes, to receive messages transmitted from the implantable medicaldevice (IMD) remote from the LCP via a second pair of the plurality ofelectrodes, and to receive cardiac signals via a third pair of theplurality of electrodes. In some cases, the first pair of electrodes,the second pair of electrodes and the third pair of electrodescorrespond to the same pair of electrodes, while in others, differentelectrodes may be used.

FIG. 4 is a schematic diagram of an illustrative subcutaneousimplantable cardioverter defibrillator (SICD) 50 that may, for example,be considered as being an example of the ICD 20 (FIG. 2). Theillustrative SICD 50 includes a housing 52 and an electrode support 54that is operably coupled to the housing 52. In some cases, the electrodesupport 54 may be configured to place one or more electrodes in aposition, such as subcutaneous or sub-sternal, that enables the one ormore electrodes to detect cardiac electrical activity as well as todeliver electrical shocks to the heart H when appropriate. In theexample shown, the housing 52 may house a controller 56, a power supply58 and a communications module 60. As illustrated, the electrode support54 includes a first electrode 62, a second electrode 64 and a thirdelectrode 66. In some cases, the electrode support 54 may include feweror more electrodes. In some cases, the SICD 50 may include one or moreother sensors such as an accelerometer or a gyro, for example.

In some cases, the controller 56 may be configured to analyze cardiacelectrical activity sensed by two or more of the electrodes 62, 64, 66and to make a determination as to whether to provide a message and/orinstruction to a leadless cardiac pacemaker (LCP), such as but notlimited to the LCP 18, 30 implanted remote from the SICD 50 and securedto the patient's heart H. In some cases, when the controller 56 makes adetermination to provide a message and/or instruction to the LCP 18, 30,the controller 56 may be configured to transmit a plurality of redundanttransmissions of the message and/or instruction by conductedcommunication during a cardiac cycle of the patient's heart. In somecases, the controller 56 may be configured to add a tracking number toeach of the plurality of redundant transmissions of the message and/orinstruction. For example, the tracking number could be as simple as “1of 3”, “2 of 3” and “3 of 3” of three sequentially transmitted redundantmessages. When such tracking numbers are added, the receiving LCP 18, 30may more easily recognize the messages as being repeated or redundantcopies of the same message. In other cases, the LCP 18, 30 may simplytreat all messages received during a predetermined time period (e.g.during a blanking period) as redundant messages of the same message.

In some cases, the ICD 20, 50 may not be capable of receivingacknowledge messages such as but not limited to conducted communicationmessages from the LCP 18, 30, due to either hardware limitations or poorcommunication vectors. In some cases, each of the plurality of redundanttransmissions of a message may include a command or instruction to theLCP 18, 30 to deliver one or more pacing pulses, and the controller 56of the SICD 50 may be configured to monitor cardiac electrical activityfor an indication that the LCP 18, 30 delivered the one or more pacingpulses. In some instances, after the controller 56 makes a determinationto provide a message to the LCP 18, 30, the controller 56 may beconfigured to transmit the plurality of redundant transmissions of themessage within a communication time period having a time duration thatis sufficiently long to allows the LCP 18, 30 to change orientationsrelative to the SICD 50 as a result of physiological changes in thepatient to result in a substantially different vector and/or signalstrength at the LCP 18, 30.

As noted, a blanking period may correspond to a portion of a cardiaccycle or may even extend over more than one cardiac cycle. FIG. 5A showsan illustrative electrocardiogram (ECG) 70 with several blanking periodsindicated thereon. In the example shown, a first blanking period 72follows an R-wave 74. A second blanking period 76 follows an R-wave 78.A third blanking period 80 follows an R-wave 82. Each of the firstblanking period 72, the second blanking period 76 and the third blankingperiod 80 are illustrated as being shorter than one cardiac cycle, witha cardiac cycle being defined as a time period between successiveR-waves. In some instances, it is contemplated that the duration of aparticular blanking period may be adjusted. In some cases, each blankingperiod 72, 76, 80 may have the same time duration. In some cases, forexample, the blanking period 72, 76, 80 may each extend over at least 10percent of a cardiac cycle, but less than an entire cardiac cycle. Eachof the blanking period 72, 76, 80 may extend over at least 20 percent ofa cardiac cycle, but less than an entire cardiac cycle. Each of theblanking period 72, 76, 80 may extend over at least 30 percent, 40percent, 60 percent or more or less of a cardiac cycle. In some cases,as illustrated in FIG. 5B, a blanking period 84 follows the R-wave 74and extends to a point beyond the next successive R-wave 78.

FIG. 6 provides a schematic illustration of a redundant message that maybe transmitted to the LCP 18, 30 by the ICD 20, 50. In the exampleshown, a R-wave 86 indicates a start of an LCP blanking period 88. Theduration of the LCP blanking period 88 may fall within a portion of acardiac cycle or may extend over more than one cardiac cycle. The SICDmay be seen as providing a redundant transmission 90 of a message and/orinstruction to the LCP. The redundant transmission 90 may be seen ashaving a first message 92 and a second message 94 separated by a pause96. As illustrated, each of the first message 92 and the second message94 include a series of pulses, pings, or chirps defining a short timeframe, a long time frame, a short time frame therebetween. It will beappreciated that this is merely illustrative, as the message may includeany number of pulses, pings or chirps, defining any number of short,long or other time frames therebetween. As can be seen, the secondmessage 94 is the same as the first message 92, and has the same patternof pulses, pings or chirps. That is, the second message 94 is redundantto the first message 92.

In some cases, and as shown in FIG. 5A, the same message(s) may bere-broadcast during each of two (or more) heat beats. This may helpincrease the time between redundant messages, and thus may allow forphysiological changes that occur over longer time periods than just oneheartbeat.

FIG. 7 depicts another illustrative leadless cardiac pacemaker (LCP)that may be implanted into a patient and may operate to deliverappropriate therapy to the heart, such as to deliver anti-tachycardiapacing (ATP) therapy, cardiac resynchronization therapy (CRT),bradycardia therapy, and/or the like. As can be seen in FIG. 7, the LCP100 may be a compact device with all components housed within the ordirectly on a housing 120. In some cases, the LCP 100 may be consideredas being an example of the LCP 18 (FIG. 2) or the LCP 30 (FIG. 3). Inthe example shown in FIG. 7, the LCP 100 may include a communicationmodule 102, a pulse generator module 104, an electrical sensing module106, a mechanical sensing module 108, a processing module 110, a battery112, and an electrode arrangement 114. The LCP 100 may include more orless modules, depending on the application.

The communication module 102 may be configured to communicate withdevices such as sensors, other medical devices such as an SICD, and/orthe like, that are located externally to the LCP 100. Such devices maybe located either external or internal to the patient's body.Irrespective of the location, external devices (i.e. external to the LCP100 but not necessarily external to the patient's body) can communicatewith the LCP 100 via communication module 102 to accomplish one or moredesired functions. For example, the LCP 100 may communicate information,such as sensed electrical signals, data, instructions, messages, R-wavedetection markers, etc., to an external medical device (e.g. SICD and/orprogrammer) through the communication module 102. The external medicaldevice may use the communicated signals, data, instructions, messages,R-wave detection markers, etc., to perform various functions, such asdetermining occurrences of arrhythmias, delivering electricalstimulation therapy, storing received data, and/or performing any othersuitable function. The LCP 100 may additionally receive information suchas signals, data, instructions and/or messages from the external medicaldevice through the communication module 102, and the LCP 100 may use thereceived signals, data, instructions and/or messages to perform variousfunctions, such as determining occurrences of arrhythmias, deliveringelectrical stimulation therapy, storing received data, and/or performingany other suitable function. The communication module 102 may beconfigured to use one or more methods for communicating with externaldevices. For example, the communication module 102 may communicate viaradiofrequency (RF) signals, inductive coupling, optical signals,acoustic signals, conducted communication signals, and/or any othersignals suitable for communication.

In the example shown in FIG. 7, the pulse generator module 104 may beelectrically connected to the electrodes 114. In some examples, the LCP100 may additionally include electrodes 114′. In such examples, thepulse generator 104 may also be electrically connected to the electrodes114′. The pulse generator module 104 may be configured to generateelectrical stimulation signals. For example, the pulse generator module104 may generate and deliver electrical stimulation signals by usingenergy stored in the battery 112 within the LCP 100 and deliver thegenerated electrical stimulation signals via the electrodes 114 and/or114′. Alternatively, or additionally, the pulse generator 104 mayinclude one or more capacitors, and the pulse generator 104 may chargethe one or more capacitors by drawing energy from the battery 112. Thepulse generator 104 may then use the energy of the one or morecapacitors to deliver the generated electrical stimulation signals viathe electrodes 114 and/or 114′. In at least some examples, the pulsegenerator 104 of the LCP 100 may include switching circuitry toselectively connect one or more of the electrodes 114 and/or 114′ to thepulse generator 104 in order to select which of the electrodes 114/114′(and/or other electrodes) the pulse generator 104 delivers theelectrical stimulation therapy. The pulse generator module 104 maygenerate and deliver electrical stimulation signals with particularfeatures or in particular sequences in order to provide one or multipleof a number of different stimulation therapies. For example, the pulsegenerator module 104 may be configured to generate electricalstimulation signals to provide electrical stimulation therapy to combatbradycardia, tachycardia, cardiac synchronization, bradycardiaarrhythmias, tachycardia arrhythmias, fibrillation arrhythmias, cardiacsynchronization arrhythmias and/or to produce any other suitableelectrical stimulation therapy. Some more common electrical stimulationtherapies include anti-tachycardia pacing (ATP) therapy, cardiacresynchronization therapy (CRT), and cardioversion/defibrillationtherapy. In some cases, the pulse generator 104 may provide acontrollable pulse energy. In some cases, the pulse generator 104 mayallow the controller to control the pulse voltage, pulse width, pulseshape or morphology, and/or any other suitable pulse characteristic.

In some examples, the LCP 100 may include an electrical sensing module106, and in some cases, a mechanical sensing module 108. The electricalsensing module 106 may be configured to sense the cardiac electricalactivity of the heart. For example, the electrical sensing module 106may be connected to the electrodes 114/114′, and the electrical sensingmodule 106 may be configured to receive cardiac electrical signalsconducted through the electrodes 114/114′. The cardiac electricalsignals may represent local information from the chamber in which theLCP 100 is implanted. For instance, if the LCP 100 is implanted within aventricle of the heart (e.g. RV, LV), cardiac electrical signals sensedby the LCP 100 through the electrodes 114/114′ may represent ventricularcardiac electrical signals. In some cases, the LCP 100 may be configuredto detect cardiac electrical signals from other chambers (e.g. farfield), such as the P-wave from the atrium.

The mechanical sensing module 108 may include one or more sensors, suchas an accelerometer, a pressure sensor, a heart sound sensor, ablood-oxygen sensor, a chemical sensor, a temperature sensor, a flowsensor and/or any other suitable sensors that are configured to measureone or more mechanical/chemical parameters of the patient. Both theelectrical sensing module 106 and the mechanical sensing module 108 maybe connected to a processing module 110, which may provide signalsrepresentative of the sensed mechanical parameters. Although describedwith respect to FIG. 7 as separate sensing modules, in some cases, theelectrical sensing module 106 and the mechanical sensing module 108 maybe combined into a single sensing module, as desired.

The electrodes 114/114′ can be secured relative to the housing 120 butexposed to the tissue and/or blood surrounding the LCP 100. In somecases, the electrodes 114 may be generally disposed on either end of theLCP 100 and may be in electrical communication with one or more of themodules 102, 104, 106, 108, and 110. The electrodes 114/114′ may besupported by the housing 120, although in some examples, the electrodes114/114′ may be connected to the housing 120 through short connectingwires such that the electrodes 114/114′ are not directly securedrelative to the housing 120. In examples where the LCP 100 includes oneor more electrodes 114′, the electrodes 114′ may in some cases bedisposed on the sides of the LCP 100, which may increase the number ofelectrodes by which the LCP 100 may sense cardiac electrical activity,deliver electrical stimulation and/or communicate with an externalmedical device. The electrodes 114/114′ can be made up of one or morebiocompatible conductive materials such as various metals or alloys thatare known to be safe for implantation within a human body. In someinstances, the electrodes 114/114′ connected to the LCP 100 may have aninsulative portion that electrically isolates the electrodes 114/114′from adjacent electrodes, the housing 120, and/or other parts of the LCP100. In some cases, one or more of the electrodes 114/114′ may beprovided on a tail (not shown) that extends away from the housing 120.

The processing module 110 can be configured to control the operation ofthe LCP 100. For example, the processing module 110 may be configured toreceive electrical signals from the electrical sensing module 106 and/orthe mechanical sensing module 108. Based on the received signals, theprocessing module 110 may determine, for example, abnormalities in theoperation of the heart H. Based on any determined abnormalities, theprocessing module 110 may control the pulse generator module 104 togenerate and deliver electrical stimulation in accordance with one ormore therapies to treat the determined abnormalities. The processingmodule 110 may further receive information from the communication module102. In some examples, the processing module 110 may use such receivedinformation to help determine whether an abnormality is occurring,determine a type of abnormality, and/or to take particular action inresponse to the information. The processing module 110 may additionallycontrol the communication module 102 to send/receive information to/fromother devices.

In some examples, the processing module 110 may include a pre-programmedchip, such as a very-large-scale integration (VLSI) chip and/or anapplication specific integrated circuit (ASIC). In such embodiments, thechip may be pre-programmed with control logic in order to control theoperation of the LCP 100. By using a pre-programmed chip, the processingmodule 110 may use less power than other programmable circuits (e.g.general purpose programmable microprocessors) while still being able tomaintain basic functionality, thereby potentially increasing the batterylife of the LCP 100. In other examples, the processing module 110 mayinclude a programmable microprocessor. Such a programmablemicroprocessor may allow a user to modify the control logic of the LCP100 even after implantation, thereby allowing for greater flexibility ofthe LCP 100 than when using a pre-programmed ASIC. In some examples, theprocessing module 110 may further include a memory, and the processingmodule 110 may store information on and read information from thememory. In other examples, the LCP 100 may include a separate memory(not shown) that is in communication with the processing module 110,such that the processing module 110 may read and write information toand from the separate memory.

The battery 112 may provide power to the LCP 100 for its operations. Insome examples, the battery 112 may be a non-rechargeable lithium-basedbattery. In other examples, a non-rechargeable battery may be made fromother suitable materials, as desired. Because the LCP 100 is animplantable device, access to the LCP 100 may be limited afterimplantation. Accordingly, it is desirable to have sufficient batterycapacity to deliver therapy over a period of treatment such as days,weeks, months, years or even decades. In some instances, the battery 112may a rechargeable battery, which may help increase the useable lifespanof the LCP 100. In still other examples, the battery 112 may be someother type of power source, as desired.

To implant the LCP 100 inside a patient's body, an operator (e.g., aphysician, clinician, etc.), may fix the LCP 100 to the cardiac tissueof the patient's heart. To facilitate fixation, the LCP 100 may includeone or more anchors 116. The anchor 116 may include any one of a numberof fixation or anchoring mechanisms. For example, the anchor 116 mayinclude one or more pins, staples, threads, screws, helix, tines, and/orthe like. In some examples, although not shown, the anchor 116 mayinclude threads on its external surface that may run along at least apartial length of the anchor 116. The threads may provide frictionbetween the cardiac tissue and the anchor to help fix the anchor 116within the cardiac tissue. In other examples, the anchor 116 may includeother structures such as barbs, spikes, or the like to facilitateengagement with the surrounding cardiac tissue.

FIG. 8 depicts an example of another or second medical device (MD) 200,which may be used in conjunction with the LCP 100 (FIG. 7) in order todetect and/or treat cardiac abnormalities. In some cases, the MD 200 maybe considered as an example of the ICD 20 (FIG. 2) or the SICD 50 (FIG.4). In the example shown, the MD 200 may include a communication module202, a pulse generator module 204, an electrical sensing module 206, amechanical sensing module 208, a processing module 210, and a battery218. Each of these modules may be similar to the modules 102, 104, 106,108, and 110 of LCP 100. Additionally, the battery 218 may be similar tothe battery 112 of the LCP 100. In some examples, however, the MD 200may have a larger volume within the housing 220. In such examples, theMD 200 may include a larger battery and/or a larger processing module210 capable of handling more complex operations than the processingmodule 110 of the LCP 100.

While it is contemplated that the MD 200 may be another leadless devicesuch as shown in FIG. 7, in some instances the MD 200 may include leadssuch as leads 212. The leads 212 may include electrical wires thatconduct electrical signals between the electrodes 214 and one or moremodules located within the housing 220. In some cases, the leads 212 maybe connected to and extend away from the housing 220 of the MD 200. Insome examples, the leads 212 are implanted on, within, or adjacent to aheart of a patient. The leads 212 may contain one or more electrodes 214positioned at various locations on the leads 212, and in some cases atvarious distances from the housing 220. Some leads 212 may only includea single electrode 214, while other leads 212 may include multipleelectrodes 214. Generally, the electrodes 214 are positioned on theleads 212 such that when the leads 212 are implanted within the patient,one or more of the electrodes 214 are positioned to perform a desiredfunction. In some cases, the one or more of the electrodes 214 may be incontact with the patient's cardiac tissue. In some cases, the one ormore of the electrodes 214 may be positioned subcutaneously and outsideof the patient's heart. In some cases, the electrodes 214 may conductintrinsically generated electrical signals to the leads 212, e.g.signals representative of intrinsic cardiac electrical activity. Theleads 212 may, in turn, conduct the received electrical signals to oneor more of the modules 202, 204, 206, and 208 of the MD 200. In somecases, the MD 200 may generate electrical stimulation signals, and theleads 212 may conduct the generated electrical stimulation signals tothe electrodes 214. The electrodes 214 may then conduct the electricalsignals and delivery the signals to the patient's heart (either directlyor indirectly).

The mechanical sensing module 208, as with the mechanical sensing module108, may contain or be electrically connected to one or more sensors,such as accelerometers, acoustic sensors, blood pressure sensors, heartsound sensors, blood-oxygen sensors, and/or other sensors which areconfigured to measure one or more mechanical/chemical parameters of theheart and/or patient. In some examples, one or more of the sensors maybe located on the leads 212, but this is not required. In some examples,one or more of the sensors may be located in the housing 220.

While not required, in some examples, the MD 200 may be an implantablemedical device. In such examples, the housing 220 of the MD 200 may beimplanted in, for example, a transthoracic region of the patient. Thehousing 220 may generally include any of a number of known materialsthat are safe for implantation in a human body and may, when implanted,hermetically seal the various components of the MD 200 from fluids andtissues of the patient's body.

In some cases, the MD 200 may be an implantable cardiac pacemaker (ICP).In this example, the MD 200 may have one or more leads, for example theleads 212, which are implanted on or within the patient's heart. The oneor more leads 212 may include one or more electrodes 214 that are incontact with cardiac tissue and/or blood of the patient's heart. The MD200 may be configured to sense intrinsically generated cardiacelectrical signals and determine, for example, one or more cardiacarrhythmias based on analysis of the sensed signals. The MD 200 may beconfigured to deliver CRT, ATP therapy, bradycardia therapy, and/orother therapy types via the leads 212 implanted within the heart. Insome examples, the MD 200 may additionally be configured providedefibrillation therapy.

In some instances, the MD 200 may be an implantablecardioverter-defibrillator (ICD). In such examples, the MD 200 mayinclude one or more leads implanted within a patient's heart. The MD 200may also be configured to sense cardiac electrical signals, determineoccurrences of tachyarrhythmias based on the sensed signals, and may beconfigured to deliver defibrillation therapy in response to determiningan occurrence of a tachyarrhythmia. In other examples, the MD 200 may bea subcutaneous implantable cardioverter-defibrillator (S-ICD). Inexamples where the MD 200 is an S-ICD, one of the leads 212 may be asubcutaneously implanted lead. In at least some examples where the MD200 is an S-ICD, the MD 200 may include only a single lead which isimplanted subcutaneously, but this is not required. In some instances,the lead(s) may have one or more electrodes that are placedsubcutaneously and outside of the chest cavity. In other examples, thelead(s) may have one or more electrodes that are placed inside of thechest cavity, such as just interior of the sternum but outside of theheart H.

In some examples, the MD 200 may not be an implantable medical device.Rather, the MD 200 may be a device external to the patient's body, andmay include skin-electrodes that are placed on a patient's body. In suchexamples, the MD 200 may be able to sense surface electrical signals(e.g. cardiac electrical signals that are generated by the heart orelectrical signals generated by a device implanted within a patient'sbody and conducted through the body to the skin). In such examples, theMD 200 may be configured to deliver various types of electricalstimulation therapy, including, for example, defibrillation therapy.

FIG. 9 illustrates an example of a medical device system and acommunication pathway through which multiple medical devices 302, 304,306, and/or 310 may communicate. In the example shown, the medicaldevice system 300 may include LCPs 302 and 304, external medical device306, and other sensors/devices 310. The external device 306 may be anyof the devices described previously with respect to the MD 200. Othersensors/devices 310 may also be any of the devices described previouslywith respect to the MD 200. In some instances, other sensors/devices 310may include a sensor, such as an accelerometer, an acoustic sensor, ablood pressure sensor, or the like. In some cases, other sensors/devices310 may include an external programmer device that may be used toprogram one or more devices of the system 300.

Various devices of the system 300 may communicate via communicationpathway 308. The communication pathway 308 may include one or a numberof different communication paths and/or a number of differentcommunication modes. The communication pathway 308 may also include oneor more distinct communication vectors. In some cases, for example, theLCPs 302 and/or 304 may sense intrinsic cardiac electrical signals andmay communicate such signals to one or more other devices 302/304, 306,and 310 of the system 300 via communication pathway 308. In one example,one or more of the devices 302/304 may receive such signals and, basedon the received signals, determine an occurrence of an arrhythmia. Insome cases, the device or devices 302/304 may communicate suchdeterminations to one or more other devices 306 and 310 of the system300. In some cases, one or more of the devices 302/304, 306, and 310 ofthe system 300 may take action based on the communicated determinationof an arrhythmia, such as by delivering a suitable electricalstimulation to the heart of the patient. It is contemplated that thecommunication pathway 308 may communicate using RF signals, inductivecoupling, optical signals, acoustic signals, or any other signalssuitable for communication. Additionally, in at least some examples,device communication pathway 308 may include multiple signal types. Forinstance, other sensors/device 310 may communicate with the externaldevice 306 using a first signal type (e.g. RF communication) butcommunicate with the LCPs 302/304 using a second signal type (e.g.conducted communication). Further, in some examples, communicationbetween devices may be limited. For instance, as described above, insome examples, the LCPs 302/304 may communicate with the external device306 only through other sensors/devices 310, where the LCPs 302/304 sendsignals to other sensors/devices 310, and other sensors/devices 310relay the received signals to the external device 306.

In some cases, the communication pathway 308 may include conductedcommunication. Accordingly, devices of the system 300 may havecomponents that allow for such conducted communication. For instance,the devices of system 300 may be configured to transmit conductedcommunication signals (e.g. current and/or voltage pulses) into thepatient's body via one or more electrodes of a transmitting device, andmay receive the conducted communication signals (e.g. pulses) via one ormore electrodes of a receiving device. The patient's body may “conduct”the conducted communication signals (e.g. pulses) from the one or moreelectrodes of the transmitting device to the electrodes of the receivingdevice in the system 300. In such examples, the delivered conductedcommunication signals (e.g. pulses) may differ from pacing or othertherapy signals. For example, the devices of the system 300 may deliverelectrical communication pulses at an amplitude/pulse width that issub-capture threshold to the heart. Although, in some cases, theamplitude/pulse width of the delivered electrical communication pulsesmay be above the capture threshold of the heart, but may be deliveredduring a blanking period of the heart (e.g. refractory period) and/ormay be incorporated in or modulated onto a pacing pulse, if desired.

Delivered electrical communication pulses may be modulated in anysuitable manner to encode communicated information. In some cases, thecommunication pulses may be pulse width modulated or amplitudemodulated. Alternatively, or in addition, the time between pulses may bemodulated to encode desired information. In some cases, conductedcommunication pulses may be voltage pulses, current pulses, biphasicvoltage pulses, biphasic current pulses, or any other suitableelectrical pulse as desired.

FIG. 10 shows an illustrative medical device system. In FIG. 10, an LCP402 is shown fixed to the interior of the left ventricle of the heart410, and a pulse generator 406 is shown coupled to a lead 412 having oneor more electrodes 408 a-408 c. In some cases, the pulse generator 406may be part of a subcutaneous implantable cardioverter-defibrillator(S-ICD), and the one or more electrodes 408 a-408 c may be positionedsubcutaneously. In some cases, the one or more electrodes 408 a-408 cmay be placed inside of the chest cavity but outside of the heart, suchas just interior of the sternum. In some cases, the LCP 402 maycommunicate with the subcutaneous implantable cardioverter-defibrillator(S-ICD). In some cases, the lead 412 and/or pulse generator 406 mayinclude an accelerometer 414 that may, for example, be configured tosense vibrations that may be indicative of heart sounds.

In some cases, the LCP 402 may be in the right ventricle, right atrium,left ventricle or left atrium of the heart, as desired. In some cases,more than one LCP 402 may be implanted. For example, one LCP may beimplanted in the right ventricle and another may be implanted in theright atrium. In another example, one LCP may be implanted in the rightventricle and another may be implanted in the left ventricle. In yetanother example, one LCP may be implanted in each of the chambers of theheart.

It should be understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of steps without exceeding the scope of thedisclosure. This may include, to the extent that it is appropriate, theuse of any of the features of one example embodiment being used in otherembodiments.

What is claimed is:
 1. A medical system comprising: a first implantablemedical device (IMD) configured to implanted in a patient's body; asecond implantable medical device (IMD) configured to be implanted in apatient's body; wherein the first IMD comprises: a housing; a pluralityof electrodes; a controller housed by the housing of the first IMD andoperably coupled to the plurality of electrodes of the first IMD, thecontroller of the first IMD is configured to sense cardiac electricalactivity via two or more of the plurality of electrodes of the firstIMD; the controller of the first IMD configured to analyze the sensedcardiac electrical activity and to make a determination as to whether totransmit a message for use by the second IMD; and wherein, when thecontroller of the first IMD makes the determination to transmit themessage for use by the second IMD, the controller is configured totransmit a plurality of transmissions of the message by conductedcommunication, resulting in transmission of at least one redundanttransmission of the message; wherein the second IMD comprises: ahousing; a plurality of electrodes; a controller housed by the housingof the second IMD and operably coupled to the plurality of electrodes ofthe second IMD, the controller of the second IMD is configured to:generate and deliver pacing pulses via a pair of the plurality ofelectrodes of the second IMD; receive messages transmitted by conductedcommunication via a pair of the plurality of electrodes of the secondIMD; and receive at least one of the plurality of transmissions of themessage transmitted by the first IMD, and when more than one of theplurality of transmissions of the message are successfully received bythe controller of the second IMD, the controller of the second IMD isconfigured to treat the more than one successfully received transmissionof the message as a single copy of the message, thereby ignoringadditional successfully received redundant transmissions of the message.2. The medical system of claim 1, wherein the controller of the firstIMD is configured to add a tracking number to each of the plurality oftransmissions of the message.
 3. The medical system of claim 1, whereinthe first IMD is incapable of receiving a conducted communicationmessage from the second IMD.
 4. The medical system of claim 1, whereineach of the plurality of transmissions of the message comprise a commandto the second IMD to deliver one or more pacing pulses, and thecontroller of the first IMD is configured to monitor cardiac electricalactivity for an indication that the second IMD delivered the one or morepacing pulses.
 5. The medical system of claim 1, wherein after thecontroller makes a determination to provide the message to the secondIMD, the controller is configured to transmit the plurality oftransmissions of the message within a communication time period, whereinthe communication time period has a time duration sufficiently long toallow the second IMD to change orientations relative to the first IMD asa result of the patient's heart beating to result in a substantiallydifferent received signal strength at the second IMD.
 6. The medicalsystem of claim 1, wherein the first IMD comprises an implantablecardioverter defibrillator (ICD).
 7. The medical system of claim 6,wherein the second IMD comprises a leadless cardiac pacemaker (LCP). 8.The medical system of claim 7, wherein the message transmitted by thefirst IMD includes an instruction that directs the controller of thesecond IMD to deliver pacing pulses in accordance with anAnti-Tachycardia-Pacing (ATP) therapy.
 9. The medical system of claim 8,wherein the controller of the first IMD make the determination totransmit the message for use by the second IMD when the controller ofthe first IMD determines that the sense cardiac electrical activityindicates a cardiac arrythmia.
 10. A medical system for sensing andregulating cardiac activity of a patient, the medical system comprising:an implantable cardioverter defibrillator (ICD) configured to senseelectrical cardiac activity of a patient's heart; a leadless cardiacpacemaker (LCP) configured to be disposable within a chamber of thepatient's heart; wherein the ICD comprises: a housing; a plurality ofelectrodes; an ICD controller housed by the housing of the ICD andoperably coupled to the plurality of electrodes of the ICD, the SICDcontroller configured to sense cardiac electrical activity via two ormore of the plurality of electrodes of the ICD; the ICD controllerfurther configured to analyze the sensed cardiac electrical activity andto make a determination as to whether to instruct the LCP to provide atherapy to the patient's heart; wherein, when the ICD controller makes adetermination to instruct the LCP to provide the therapy to thepatient's heart, the ICD controller is configured to transmit aplurality of transmissions of an instruction resulting in transmissionof at least one redundant transmission of the instruction; wherein theLCP comprises: a housing; a plurality of electrodes exposed external tothe housing of the LCP; an LCP controller housed by the housing of theLCP and operably coupled to the plurality of electrodes of the LCP, theLCP controller configured to: generate and deliver pacing pulses via twoor more of the plurality of electrodes of the LCP; receive cardiacsignals via two or more of the plurality of electrodes of the LCP; andwherein the LCP controller is further configured to receive at least oneof the plurality of transmissions of the instruction transmitted by theICD via two or more of the plurality of electrodes of the LCP, and whenmore than one of the plurality of transmissions of the instruction aresuccessfully received by the LCP controller, the LCP controller isconfigured to treat the more than one transmissions of the instructionas a single copy of the instruction, thereby ignoring additionalsuccessfully received redundant transmissions of the instruction andonly executing the single copy of the instruction and not each of theplurality of transmissions of the instruction.
 11. The medical system ofclaim 10, wherein the ICD controller is configured to add a trackingnumber to each of the plurality of transmissions of the instruction. 12.The medical system of claim 10, wherein the ICD is incapable ofreceiving a conducted communication message from the LCP.
 13. Themedical system of claim 10, wherein each of the plurality oftransmissions of the instruction comprise an instruction to the LCPcontroller to deliver one or more pacing pulses via two or more of theplurality of electrodes of the LCP.
 14. The medical system of claim 13,wherein the ICD controller is configured to monitor cardiac electricalactivity for an indication that the LCP delivered the one or more pacingpulses.
 15. The medical system of claim 10, wherein each of theplurality of transmissions of the instruction comprise an instruction tothe LCP controller to deliver one or more pacing pulses via two or moreof the plurality of electrodes of the LCP in accordance with anAnti-Tachycardia-Pacing (ATP) therapy.
 16. The medical system of claim15, wherein the ICD controller makes the determination to instruct theLCP to provide the therapy to the patient's heart when the ICDcontroller determines that the sense cardiac electrical activityindicates a cardiac arrythmia.
 17. The medical system of claim 10,wherein after the ICD controller makes a determination to instruct theLCP to provide the therapy to the patient's heart, the ICD controller isconfigured to transmit the plurality of transmissions of the instructionwithin a communication time period, wherein the communication timeperiod has a time duration sufficiently long to allow the LCP to changeorientations relative to the ICD as a result of the patient's heartbeating to result in a substantially different received signal strengthat the LCP.
 18. A method comprising: receiving a signal indicative ofcardiac activity at a first IMD; analyzing the signal to determinewhether to transmit an instruction; when it is determined to transmitthe instruction, transmitting a plurality of transmissions of theinstruction by the first IMD, resulting in transmission of at least oneredundant transmission of the instruction; receiving by a second IMD atleast one of the plurality of transmissions of the instructiontransmitted by the first IMD, and when more than one of the plurality oftransmissions of the instruction are successfully received by the secondIMD, treating the more than one successfully received transmission ofthe instruction as a single copy of the instruction, thereby ignoringadditional successfully received redundant transmissions of theinstruction; and executing the received instruction by the second IMD.19. The method of claim 18, wherein the first IMD comprises animplantable cardioverter defibrillator (ICD) and the second IMDcomprises a leadless cardiac pacemaker (LCP).
 20. The method of claim19, wherein the instruction transmitted by the first IMD includes aninstruction that directs the second IMD to deliver pacing pulses inaccordance with an Anti-Tachycardia-Pacing (ATP) therapy.